1. Field of the Invention
This invention relates to exit devices using latch mechanisms mortised into the door, particularly mortise latch mechanisms used in combination with vertical rod latch assemblies. More specifically, this invention relates to mortise latch mechanisms suitable for use in both single and double door installations.
2. Description of Related Art
Exit devices using vertical rod mechanisms to latch the door at the top and bottom are widely used in public buildings, particularly where provision must be made for rapid operation in an emergency to evacuate the building. Such devices usually employ a push rail, a push bar, an emergency push plate or a similar type of opening mechanism that operates with inward pressure. This allows the exit device to open quickly and reliably under the pressure of a large number of people trying to exit the building in an emergency.
Vertical rod exit devices are often used on double door installations where both doors can be opened to provide a large and unobstructed exit. Conventional vertical rod exit devices, however, suffer from numerous problems. Typically, the vertical rod exit device will have two externally mounted vertical rods. One vertical rod will extend upward from the push rail to a latch mechanism mounted near the upper edge of the door. The upper latch will engage a strike plate set into the frame above the door. A second vertical rod will extend vertically downward to a latch mechanism mounted near the bottom edge of the door. The lower latch will engage a strike plate set into the floor.
One problem with this design is that the downwardly extending rod, when surface mounted on the door, will interfere with the use of the door. The lower rod tends to catch and obstruct wheelchairs and carts passing through the door, particularly when the door is provided with an automatic closure device that continuously urges the door towards the closed position. This pressure forces the face of the door and the surface mounted lower vertical rod into the path of the cart or wheelchair. Although vertical rod designs are known in which the rods are mounted inside the door, such solutions are expensive and not easily retrofitted to existing doors.
Another difficulty with the lower vertical rod is that the bottom latch must engage a strike plate in the floor. The floor mounted strike plate poses a tripping hazard which is a liability concern.
Removal of the lower rod, however, compromises the security of the door as the door is now latched only by the upper latch. The length of the door allows significant force to be exerted against the single upper latch. One solution to this security problem is to use a center latch mechanism in combination with the upper vertical rod latch. A mortise latch design for the center latch is considered to be one of the more secure types of latch for use at the center position. While this arrangement (a single vertical rod latch at the top and a center latch) is effective in single door applications, the center latch causes difficulties in double door applications.
The principal difficulty with prior art double door applications has been in coordinating operation of the center latch when the two doors are used independently. In double door designs with only vertical rod latches and no center latch, the double doors may be identical mirror images, with each one operating independently of the other. In double door designs using a center latch however, one of the two doors will be an active door, including a latch bolt which extends out from the active door and engages an opening in the passive door. It Is this active latch bolt that causes the difficulty because it needs to be retracted when either door is being opened or closed.
In one design for center latched vertical rod double doors, the latch bolt on the active door is retracted by the opening mechanism on the active door (usually a push rail) and is spring loaded with an inclined strike surface so that it automatically retracts when the active door closes against an angled strike plate on the closed passive door. In this design, the passive door is manually latched in position at the top and bottom and can only be opened or closed when the active door is being held open. Because the passive door lacks a push rail opening mechanism, and cannot be closed when the active door is closed, it cannot function as a conventional door and is of limited value in an emergency.
Other improved designs allow the passive door to be opened regardless of the state of the active door, as needed in an emergency, but the passive door still cannot be closed unless the active door is held open. Thus, these designs do not allow the passive door to be used for normal operation. Heretofore, all double door vertical rod systems employing a center latch mechanism have had some limitation on the order of opening or closing the passive door relative to the open or closed position of the active door.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a mortise style center latch mechanism suitable for use in single and double door applications and for use in combination with single or double vertical rod latch mechanisms which allows each door of a double door combination to be operated independently without regard to the open or closed position of the other door.